Cooling medium for use at elevated temperatures

ABSTRACT

A coolant containing 35-65 wt. % polyethylene glycol and 65-35 wt. % ethylene glycol, which is especially useful for cooling motor vehicle engines.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to cooling mediums at elevated temperatures, such as 130° C.

2. Description of the Prior Art

Heat-stabilized, glass-fibre-reinforced polyamide (PA) 66 is successfully used throughout the world in motor vehicle coolant systems. The economical and efficient manufacture of cooling water tanks, water pipes and thermostatic valve housings in addition to high dynamic loading capacity and resistance to the cooling medium at 108° C. predestines PA 66 for this field of application. Development work to increase the efficiency of internal combustion engines expects higher temperature stresses in the cooling medium. Demands on mechanical properties following contact with the cooling medium at 130° C. are increasing.

A mixture comprising ethylene glycol:water in the ratio 1:1 is described as cooling medium in the motor vehicle field. The mixture solidifies at −30° C. and boils at 108° C. Azeotropic distillation is not involved. First of all, the water distils off at 108° C. The temperature of the boiling material increases as the ethylene glycol content increases, until pure glycol distils at 197.4° C.

If the temperature of the cooling medium in the closed cooling system rises to 130° C., the internal pressure rises to 2 bars. With the increase in the operating temperature of the cooling medium, in addition to very good tightness, high mechanical strength values at 130° C. in the state saturated with cooling medium are a prerequisite for the operation of the cooling system. If part of the cooling medium escapes as steam, the ethylene glycol content in the cooling medium increases. Components made of polyamide may partially dissolve if glycol content and temperature increase perceptibly.

The object of the invention was therefore to develop a cooling medium which operates at the desired temperatures (approx. 130° C.) without pressure increase and does not perceptibly impair the mechanical properties of polyamide.

The invention provides a cooling medium containing

A) 35-65, preferably 45 to 55 wt. % of polyethylene glycol

B) 35-65, preferably 45 to 55 wt. % of ethylene glycol.

The cooling medium is suitable for cooling motor vehicle engines.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Polyethylene glycols of the formula HO—(CH₂—CH₂—O)_(n)—H, with an average molar mass between 285 and 420 g/mol, a hydrolysis value between 271-315 and a density between 1.12-1.15 g/cm³ are suitable as polyethylene glycol (A) of the mixture according to the invention.

Technical ethylene glycols of the formula HO—CH₂—CH₂—OH, a molar weight of 60.05 g/mol and a density of 1.10 to 1.13 g/cm³ are suitable as ethylene glycol (B) of the mixture according to the invention.

Stabilizers may additionally be added to the mixture.

Metal deactivators, phosphites and anti-oxidants, such as are conventionally used in the stabilization of a cooling medium, are suitable as stabilizer. The stabilizer is conventionally added in quantities up to 2 wt. %, related to 100 wt. % of mixture comprising A) and B).

It has surprisingly been found that glass-fibre-reinforced PA 6 is also resistant to this cooling medium at 130° C. PA 6 can therefore also be used for the manufacture of components in the cooling system, such as cooling water tanks, thermostatic valve housings, cooling water pipes.

The glass fibre content is generally 25-45 wt. %, preferably 30-35 wt. % (related to the total moulding compound).

EXAMPLES

The following products are used in the examples:

PA 66 GF 30=Durethane AKV 30 HR H 2.0 9005/0, Bayer AG

PA 6 GF 30=Durethane BKV 30 H 2.0 9005/0, Bayer AG Pseudoplastic

PA 6 GF 30=Durethane KU 2-2140/30 H 2.0 9005/0, Bayer AG

Polyglycol 300=Polyethylene glycol 300, e.g. Hoechst or Merck

Polyglycol 400=Polyethylene glycol 400, e.g. Hoechst or Merck

Ethylene glycol=Ethanediol

Example 1 (Comparison)

Test bodies made of Durethane AKV 30 HR H 2.0 9005/0 (Bayer AG) are stored in a cooling medium, consisting of ethanediol:water in the weight ratio 1:1, in an autoclave.

The autoclave is half-filled with cooling medium (ethanediol:water in the ratio 1:1) as tempering fluid. The test bodies are stored separately in the cooling medium in special steel containers. At 130° C. the pressure gauge gives a pressure reading of 2 bars. The heating is switched off after 10, 21 and 40 days. After a cooling time of 16 hours, the test bodies are removed, washed with water, dried, weighed and tested within three hours. The results obtained are summarized in Table 1.

Example 2

Test bodies made of Durethane AKV 30 HR H 2.0 9005/0 (Bayer AG) are stored in a flask with reflux condenser, in a cooling medium consisting of ethanediol:polyglycol 300 (1:1). The flask is heated by means of an oil bath at 137° C. The temperature of the cooling medium is constantly kept at 130° C. The test bodies are removed after 10, 21 and 40 days, cooled in cold cooling medium, washed with water, dried, weighed and tested within three hours. The results obtained are summarized in Table 1.

Example 3

The tests in Example 2 are repeated. The storage tests take place at a cooling medium temperature of 150° C. The results obtained are summarized in Table 1.

Examples 4 and 5

Example 1 is repeated with test bodies made of Durethane KU 2-2140/30 instead of AKV 30 HR at 130 and 120° C. The results obtained are summarized in Table 2.

Example 6

Example 2 is repeated with test bodies made of Durethane KU 2-2140/30 H 2.0 and BKV 30 H 2.0 9005/0 instead of AKV 30 HR at 130° C. The results obtained are summarized in Table 2.

TABLE 1 Mechanical properties of AKV 30 HR H 2.0 9005/0 after storage in various cooling media at 130° C. and 150° C. Example No. 1 (comparison) 2 3 Cooling Days Glycol:water Polyglycol: Polyglycol: medium (d) (1:1) glycol glycol (1:1) (1:1) Temp./ ° C./ 130/2 130/1 150/1 pressure bars Weight % 0 d 11 8 9 increase 21 d 11 8 9 42 d 11 8 9 Impact kJ/m² 0 d 61 61 61 strength 10 d 57 100 88 ISO 180 1C 21 d 54 83 59 42 d 17 61 25 Tear strength MPa 0 d 181 181 181 ISO 527 10 d 75 104 99 21 d 66 101 95 42 d 32 98 54 Elongation % 0 d 3.9 3.9 3.9 at tear 10 d 4.8 7.3 6.0 ISO 527 21 d 3.2 5.4 5.0 42 d 1.1 4.2 1.8 Tensile E MPa 0 d 9330 9330 9330 modulus 10 d 3790 4490 4500 DIN 53457-1 21 d 3870 4500 4500 42 d 3670 4780 4270 Bending MPa 0 d 281 281 281 strength 10 d 107 145 139 ISO 178 21 d 84 147 109 42 d 36 136 58 Outer fibre % 0 d 4.8 4.8 4.8 strain 10 d 5.7 7.6 7.3 ISO 178 21 d 3.7 7.4 4.5 42 d 1.5 5.7 2.6 Bending E MPa 0 d 8590 8590 8590 modulus 10 d 3300 3980 3810 ISO 178 21 d 3340 4000 3750 42 d 3110 4120 3310

TABLE 2 Mechanical properties of BKV 30 H 2.0 9005/0 and KU 2-2140/30 H 2.0 9005/0 after storage in various cooling media at 120° C. and 130° C. Example 4 5 6 7 Polyamide KU-2 KU 2- KU 2- BKV 30 2140/30 2140/30 2140/30 Cooling Days Glycol: Glycol: Polyglycol: Polyglycol: medium (d) water water glycol glycol (1:1) (1:1) (1:1) (1:1) Temp./ ° C./ 120/1.6 130/2 130/1 130/1 pressure bars Weight % 10 d 12 11 10 10 increase 21 d 11 11 10 10 42 d 12 11 10 10 Impact kJ/m² 0 d 67 67 67 65 strength 10 d 67 35 80 84 ISO 180 21 d 51 13 67 69 IC 42 d 19 — 49 50 Tear MPa 0 d 176 176 176 170 strength 10 d 69 52 86 87 ISO 527 21 d 66 26 87 84 42 d 33 — 83 80 Elongation % 0 d 3 3 3 3.3 at tear 10 d 5.6 3.1 6.2 7.2 ISO 527 21 d 4.6 0.9 5.8 6.1 42 d 1.2 — 4.7 4.2 Tensile E MPa 0 d 10710 10710 10710 9580 modulus 10 d 3670 3830 4190 4000 DIN 21 d 3920 3670 4340 4140 53457-1 42 d 3790 — 4430 4190 Bending MPa 0 d 262 262 262 260 strength 10 d 97 72 118 123 ISO 178 21 d 93 35 115 120 42 d 40 — 90 95 Outer % 0 d 4.1 4.1 4.1 4 fibre 10 d 6.8 4 7.5 7.3 strain 21 d 5.6 1.4 6.5 6.3 ISO 178 42 d 1.7 — 4.2 4.7 Bending E MPa 0 d 8610 8610 8610 8410 modulus 10 d 3180 3170 3530 3630 ISO 178 21 d 3400 3125 390 3670 42 d 3220 — 3660 3670

From Example 1 (comparative test) in Table 1 it can be seen that:

1) the internal pressure in the cooling system rises to 2 bars;

2) impact strength, tear strength and bending strength decrease steadily with the storage period;

3) the modulus values drop in the course of saturation with cooling medium and remain at the level reached;

4) the elongation values rise only through saturation with cooling medium and then drop as a result of surface decomposition.

Examples 2 and 3 show that:

1) the weight increase on storage in the cooling medium claimed is lower than in the comparative test (Example 1) at both 130° C. and 150° C.;

2) there is no pressure increase at temperatures up to 150° C.;

3) the properties after storage at 130° C. are distinctly higher than in the comparative test and still perceptibly higher at 150° C.

From Table 2 it can be seen that:

1) when stored in the standard cooling medium Durethane KU 2-2140/30/pseudoplastic PA 6 GF 30 can only be used up to 120° C. (pressure rise to 1.6 bars);

2) for both Durethane KU 2-2140/30 and the standard PA 6 GF 30 (Durethane BKV 30), the properties after storage at 130° C. in the cooling medium claimed are at a distinctly higher level than in the comparative test (Example 1 in Table 1). 

What is claimed is:
 1. A cooling medium consisting essentially of: A) 35-65 wt. % of a polyethylene glycol having an average molar mass of between 285 and 420 g/mol, B) 35-65 wt. % of ethylene glycol, and C) optionally, at least one stabilizer.
 2. The cooling medium according to claim 1, wherein the polyethylene glycol has the formula HO—(CH₂—CH₂—O)_(n)—H, a hydrolysis value of between 271 and 315, and a density of between 1.12 and 1.15 g/cm³.
 3. The cooling medium according to claim 1, wherein the at least one stabilizer consists essentially of a metal deactivator, a phosphite, am anti-oxidant, or a mixture thereof.
 4. The cooling medium according to claim 3, wherein the at least one stabilizer is present in an amount of up to 2 wt. %, based on the total weight of components (A) and (B).
 5. The cooling medium according to claim 1, where component (A) and component (B) are present in about a 1:1 ratio.
 6. The cooling medium according to claim 1, wherein component (A) contains 45 to 55 wt. % of the polyethylene glycol.
 7. The cooling medium according to claim 6, wherein component (B) contains 45 to 55 wt. % of the ethylene glycol.
 8. The cooling medium according to claim 1, wherein component (B) contains 45 to 55 wt. % of the ethylene glycol.
 9. The cooling medium according to claim 1, which is essentially free of water.
 10. A cooling medium consisting of: A) 35-65 wt. % of a polyethylene glycol having an average molar mass of between 285 and 420 g/mol, B) 35-65 wt. % of ethylene glycol, and C) optionally, at least one stabilizer. 